Device for locking a tow bar together with a steering member

ABSTRACT

A device for locking a tow bar together with a steering member of running wheels, comprises a vertical king pin secured to the end portion of a trailer body, a steering member and engaging member both rotatably supported by said king pin, said engaging member rigidly connected with one end of a tow bar, said steering and engaging members having respective slits, a slide member inserted into said slits, and means for shifting said slide member in said slits so as to cause the slide member to be engaged with said steering and engaging members at a locking portion and disengaged from said members at a releasing portion, whereby the train of trailers keep away from taking the jackknife effect.

United States Patent Hanaoka [75] Inventor: Hiroshi Hanaoka, Tokyo, Japan [73] Assignee: Hanaoka Sharyo Company Limited,

Tokyo, Japan [22] Filed: Apr. 28, 1972 [21] Appl, No.: 248,578

[30] Foreign Application Priority Data May 1, 1971 Japan 46-29301 Oct. 30, 1971 Japan 46-86582 Oct. 30, 1971 Japan 46-101394 Oct. 30, 1971 Japan 46-101395 [52] US. Cl. 280/99, 280/445 [51] Int. Cl B62d 13/06 [58] Field of Search 280/99, 445, 432

[56] References Cited UNITED STATES PATENTS 1,312,788 8/1919 Keller 280/445 2,259,923 10/1941 Byrne 280/432 3,211,467 10/1965 Siddall 280/445 3,529,848 9/1970 Harvey 280/445 3,620,549 10/1969 Miller 280/445 [111 3,853,330 [451 Dec. 10, 1974 FOREIGN PATENTS OR APPLICATIONS 307,950 3/1933 Italy 280/445 1,312,755 11/1962 France 280/99 526,051 9/ 1940 Great Britain 280/99 Roberts & Sutherland [57] ABSTRACT A device for locking a tow bar together with a steering member of running wheels, comprises a vertical king pin secured to the end portion of a trailer body, a steering member and engaging member both rotatably supported by said king pin, said engaging member rigidly connected with one end of a tow bar, said steering and engaging members having respective slits, a slide member inserted into said slits, and means for shifting said slide member in said slits so as to cause the slide member to be engaged with said steering and engaging members at a locking portion and disengaged from said members at a releasing portion, whereby the train of trailers keep away from taking the jack-knife effect.

6 Claims, 15 Drawing Figures PATENTEL 25B 1 0 I974 3. 853 .330

saw 03 or 11 PATENIEB DEC] 0 I974 saw on or 11 PATENTEU 1 74 sum user 11 PATENTEB m 1 H 74 sum o7ur11 FIG-8' PATENIEL SE8 1 01974 ssm naur 11 PATENTEB BEE l 0l974 sum as or 11 PAIENIE :12 1 0 2974 sum 10 or 1 1 DEVICE FOR LOCKING A TOW BAR TOGETHER WITH A STEERING MEMBER DETAILED DESCRIPTION OF THE INVENTION:

This invention relates to a device for locking a tow bar together with a steering member of running wheels so that the train of trailers keep away from taking the jack-knife effect.

An object of this invention is to provide an improved device for locking a tow bar together with a steering member of running wheels, wherein the locking and unlocking of the tow bar are accomplished by sliding a pin in slits which are respectively formed at a steering member and engaging member both rotatably supported by a king pin, said engaging member rigidly connected with the tow bar.

A second object of this invention is to provide an improved device for automatically locking a tow bar together with a steering member of running wheels and unlocking the former from the latter by use of the traction power applied to the train of trailers coupled.

A third object of this invention is to provide an improved device for automatically locking a tow bar together with a steering member of running wheels and unlocking the former from the latter with a caster tumable when it trails on the ground by the traction power applied to the train of trailers coupled.

A fourth object of this invention is to provide an improved device for locking a tow bar together with a steering member of running wheels positioned at the foreside of the trailer body when a trailer runs, and simultaneously unlocking another tow bar from another steering member of running wheels positioned at the backside of the trailer body when said trailer runs, by use of a manual lever.

The features and advantages of this invention will be apperently understood from the following description in reference to the accompanying drawings as follows:

FIG. 1a is a plan view of a trailer equipped with a device for locking a tow bar together with a steering member of running wheels embodying the present invention;

FIG. lb is a plan view of a shifting action assembly involved in said locking device of FIG. la;

FIG. 2 is a side view of said trailer of FIG. la;

FIG. 3 is a perspective view of an essential part of said locking device of FIG. la which is partly demounted;

FIG. 4 is a plan view of said locking device illustrated in FIG. 3 which is partly cut and removed;

FIG. 5 is a side view of said locking device illustrated in FIG. 3 which is partly cut off;

FIG. 6 is a perspective view of an essential part of said shifting action assembly illustrated in FIG. lb;

FIG. 7 is a perspective view of a spring damper involved in said shifting action assembly of FIG. lb;

FIG. 8 is a perspective view of a locking device moditied from that of FIG. 3;

FIG. 9a is a plan view of a shifting action assembly modified from that of FIG. lb;

FIG. 9b is a perspective view of an essential part of said shifting action assembly illustrated in FIG. 90;

FIG. 10 is a plan view of another embodiment of a locking device;

FIG. 11 is a perspective view of an essential part of said locking device illustrated in FIG. 10;

FIG. 12 is a perspective view of a part of a shifting action assembly involved in said locking device of FIG. 10;

and FIG. 13 is a plan view of a manual shifting action assembly involved in the other embodiment of this invention.

FIGS. la to 7 illustrates an embodiment of this invention, wherein a trailer comprises a trailer body 1 with four wheels 2 separated into two groups each of which is operatably supported under said trailer body 1 by means of knuckle joints 3. At the center portion of said trailer body 1 is positioned a vertical pivot shaft 4 by which is rotatably supported a turn table 5. Said turn table 5 has a circular rail 6 attached to the under portion thereof and carried on supporting rollers 7 pivoted to the frame of said trailer body 1 by means of horizontal pins respectively. Said turn table 5 is constituted by a main cross beam 5a, two longitudinal beams 5b horizontally extending across said beam 5a, two edge frames 50 formed along the circumference of said turn table 5, a flat floor plate 5d disposed between said beams 5b, and a plurality of rollers 5e pivotally disposed transversely between said beam Sb and edge frame 50 so as to be formed into a roller table.

With both end portions of said trailer body are provided couplers 8 each of which is involved in a device for locking a tow bar 9 together with a steering member 10 for operating the above mentioned running wheels 2 being one of the groups.

Said locking device comprises a set pin 11 operable as a king pin of said coupler 8 and vertically supported to the end portion of said trailer body 1, an engaging member 12 rotatably supported by said set pin 11 and formed into a box, and slide member 13 inserted into slits 14 and 15. Said slit 14 is formed to the bottom portion of said engaging member 12 and has a locking portion positioned at one end thereof and a releasing portion 14b positioned at the other part thereof. Preferably, said slit 14 is formed substantially into a sectorial shape, at the basic point of which is positioned said locking portion 14a. Said slit 15 is formed to said steering member 10 in a manner to extend in a longitudinal direction of the trailer. Said steering member 10 is also rotatably supported by said set pin 11 and involved in said locking device.

Said slide member 13 is preferably formed into a pin structure. There is provided means for shifting said slide member 13 from said locking portion 14a to said releasing portion 14b and vice versa. Said shifting means is particularly illustrated in FIG. 1b. Said shifting means cmprises two bell cranks 16 and 17, a connecting rod 18, a spring damper 19, a shift member 20 and a caster assembly 21. Said bell crank 16 involves a vertical pivot 16a rotatably supported by a bearing 22 mounted on the side portion of said steering member 10, a shift arm 16b one end of which is attached to the upper portion of said pivot 16a and the other end of which is attached to the lower end of said slide pin 13 projecting downwardly from said slits 14 and 15, and a swingable arm 16c one end of which is attached to the lower portion of said pivot 16a and the other end of which is pivoted to one end of said connecting rod 18. To the other end of said connecting rod 18 is pivoted one end of said bell crank 17, the pivot joint 17a of which is rotatably secured to the frame of said trailer body 1. To the other end of said bell crank 17 is pivoted one end of a rod member 19a involved in said damper 19. Said damper 19 further involved another rod member 19b having its end pivotally connected with said shift member 20, a hollow cylinder 19c attached to the other end of said rod member 19b, piston member 19d attached to the other end of said rod member 190 and having a head l9e slidably inserted into said cylinder 19c, and means of a coiled spring member 19f for biasing or urging the head 19c toward the bottom of said cylinder 19c.

It this embodiment, said shift member 20 consists of a U-shaped cam follower 20a, and a swingable lever 20b, one end of which is fixed to said cam follower 20a and the other end of which is rotatably supported to the under portion of said trailer body 1 by means of a pivot 23. Said cam follower is further used in common to both locking devices disposed to both end portions of one trailer, in such a manner that said shift member 20 is connected with the respective dampers 19 belong to the respective locking devices.

Said caster assembly 21 is provided with a cam 21a formed into a sectorial shape and co-operable with the above mentioned follower 20a, a shaft 21b turnable about a vertical axis and supported by a thrust bearing 24 fixed to the under portion of the trailer frame, the upper end of said shaft 21b being attached to the basic point portion of said cam 21a, a supporting member 210 pivotally supported to said shaft 21b by means of a horizontal pin, a caster wheel 21d carried to the legs of said supporting member 210 by means of a horizontal pivot shaft 21e spaced to said vertical axis on a horizontal plane, and means for urging said caster wheel 21d downwards to be depressed to the ground. Said urging means is, for example in this embodiment, constituted by a coiled tension spring member 21f bridging said supporting member 210 and a bush 21g prepared with said shaft 21b. Accordingly, when the caster is turned about said vertical axis by a spin motion applied to the shaft 21b as the caster wheel 21d trailing on the ground, the cam 21a shifts the cam follower along a circular line drawn by the swing of the lever 20b.

The abovementioned knuckle joint 3 involves a vertical knuckle pin 30 rotatably supported by a bearing 25 mounted on the transverse beam of the trailer body 1, said knuckle pin 3a having a bearing to which is journaled the axle of the running wheel'2, a knuckle arm 3b attached to said knuckle pin 3a to extend in a horizontal direction, and a link rod 3c both ends of which are pivoted to the free end of the knuckle arm 3b and the backside portion of the steering member 10 respectively. Accordingly, when the steering member 10 is rotated around the king pin 11, the right and left running wheels associated with said steering member 10 via the respective knuckle joints 3 are directed right and left to the longitudinal direction of the trailer body 1.

The above mentioned tow bar 9 is detachably connected with said engaging member 12 by a coupling assembly 26. Said coupling assembly 26 involves a bar stay 27, a joint rod 28, a locking device 29 for detachably engaging said joint rod 28 with the engaging member 12, and a connecting device 30 for connecting said tow bar 9 with said bar stay 27.

Said bar stay 27 has a flat place 27a on which the tow bar 9 is layed, lugs 27b extending backwards from the both sides of said bar stay 27 and having pivot holes 270, and a pivot pin 27d inserted through said holes 27c and by which the joint rod 28 is connected with said bar stay 27. l

Said locking device 29 consists of a pair of through holes 29a formed to the side walls of the box-shaped engaging member 12, a pair of lock pins 29b slidably inserted into said through holes 29a respectively and having holes for receiving stop members 29, a transverse shaft 29d joumaled to bearings 31 mounted on the upper wall of the engaging member 12, a bar lever 29e fixedly attached to the end of said shaft 29d, arm members 29f attached to both ends of said shaft 29d, links 29g pivoted to the free ends of said arms 29f and the basic ends of said stop members 29c, and means of a torsion spring member 29h for urging said shaft 29d in a rotating direction so as to cause the stop member 290 to be forcedly inserted into the hole of said lock pin 29b via a hole 12a formed to a side housing 12b of the engaging member 12. In order to connect the joint rod 28 with the engaging member 12, the lock pins 29b are inserted through the holes 29a in a manner to put the forward end of the lock pins 29b in slits 28a formed at the end of said joint rod 28, and the stop members 290 are caused in an engaging condition.

Said connecting device 30 consists of a vertical connecting pin 30a extending upwards from the flat place 27a and having a cross hole 30b, a coiled compression spring 300, and a stop pin 30d removably inserted into said bore 30b. Said tow bar 9 is provided with a hole formed at the end portion thereof, and a cap 9b screwed to said tow bar 9, said cap 9b having a hole 90 for guiding the head of the pin 30a upwards therethrough, a horizontal groove 9d for receiving said stop pin 30d and annular shoulder 9e for supporting the upper end of said spring 30c. in order to connect the tow bar 9 with the bar stay 27, the first, the pin 30a is inserted through the holes 9a and 9c, and nextly the stop pin 30d inserted into the cross hole 30b with it sliding in the groove 9d. I

In operation, when the train of the trailers is drawn in a reverse direction, the caster is, as already explained, turned around the vertical axis due to a spin motion applied to the shaft 21b, with the caster wheel 21d trailing and depressed on the ground by means of the bias spring 21f, so as to cause the cam 21a to be turned.

The rotation of said cam 21a results in shifting the shift member 20, and consequently causes the shifting action assemblies associated with the cam follower 20a in such a manner that the slide pin 13, positioned at the foreside end of the trailer body when the trailer runs, is forcedly guided to the locking portion thereby to cause the engaging manner 12 together with the steering member 10 in a locking condition, and simultaneously the slide pin 13, positioned at the backside end of the trailer body, is forcedly guided to the releasing portion 14b thereby to cause the engaging member to be free from the steering member 10. Such operation keeps the train of the trailers away from suffering the jack-knife effect.

As the train of the trailers run along a curved line, the damper 19 can be operated so as to absorb the drawing and retracting motions applied to the shifting action assembly by the steering member 10 rotating about the king pin 11.

in addition of the explanation according to this embodiment, said steering members 10 disposed to both ends of one trailer body 1 are generally associated with each other by means of an interlocking member or rod 32 to the ends of which are respectively pivoted "arms a projecting from the sides of the respective steering members 10. I

FIG. 8 indicates a coupler involving a device for locking a tow bar together with a steering member, said coupler being simplified in comparison with the structure of the coupler described in the first embodiment. In the coupler illustrated in FIG. 8, a bar stay 127 is particularly connected with an engaging member 112. Namely, said bar stay 127 also has a flat place 127a on which a tow bar 109 is layed, lugs 127b extending backwards from the both sides of said bar stay 127 and having pivot holes 127C, and a pivot pin 127d inserted through said holes 1270, and said pivot pin 127d penetrates both side walls of the engaging member 112. Said tow bar 109 can be connected with said bar stay 127 by a connecting pin 130 inserted into a bore 109a drilled to said tow bar 109.

In this embodiment, the bar stay may be replaced by a tow bar having the same structure as said bar stay.

The other parts of said coupling device are not explained for avoiding the complication, but illustrated in the drawing by reference numbers involving the same digits as those of the parts of the first embodiment, together with one digit in a third place.

FIGS. 9a and 9b indicate another embodiment of the shifting action assembly wherein the actuator involving the cam 21a and cam follower a in the first embodiment is replaced by a different actuator as described hereinafter. The other parts of the shifting assembly and the structure associated therewith are only illustrated in the drawings by reference numbers involving the same digits as those of the parts of the first embodiment, together with two digit in a third place.

Said actuator is illustrated by a reference number of 200 and comprises a shift member 220 associated with a slide member 213 and movable in a direct line, two ratchet teeth 220a formed with both sides of said shift member 220, two ratchet members 220b pivoted to the frame of a trailer body 201 and alternately engageable with said ratchet teeth 220a, and means for urging said ratchet members 220b to said shift member 220, for example, a tension spring member 2200 bridging said ratchet members.

A caster assembly according to'this embodiment is provided with the same members as those of the caster assembly 21 of the first embodiment, that is, a caster wheel 221d with a pivot shaft 221b, a bearing member 2210 supported by the trailer body of frame rotatably around a vertical axis and bearing said shaft 221b and a turning cam 221a secured to said bearing member 2210 and alternately pushing the ratchet members 220b to be disengaged from the corresponding ratchet teeth 220a and means for urging said caster wheel 221d downwards to be depressed to'the ground.

Accordingly, when the train of the trailers in drawn in a reverse direction, the caster is turned together with the cam about said vertical axis due to a spin motion applied to the shaft 221b, with the caster wheel 221d trailing and depressed on the ground.

FIGS. 10 and 12 indicate another embodiment of this invention. A device for locking a tow bar together with a steering member in accordance with this embodiment comprises two vertical set pins 301 secured to both end portions of a trailer body 302 with a turn table 303, steering members 304 rotatably supported by said set pins 301 respectively, said steering member 304 having contact portions 304apositioned at both side thereof, and engaging members 305 rigidly connected with the corresponding tow bars 306 respectively. Said engaging member 305 has pushing portions 305a positioned at both sides thereof in a manner to face the contact portions 304a of the corresponding steering member 304.

Said locking device further involves a shift member or rod 307 both ends of which are pivoted to engaging members 305 respectively, means for guiding said shift member 307 movable along a longitudinal direction of the trailer body 302, and means for automatically moving said shift member until the pushing portions 305a positioned at the foreside of the trailer body 302 when the trailer runs, are brought into contact with the contact portions 304a of the corresponding steering member, and maintaining its'contact position.

Said guiding means consists of a plurality of slide bores 308 drilled to transverse beams 309 of the trailer body 302, so that the shift member 307 is slidably inserted through said bores 308.

Said means for automatically moving said shift member 307 and maintaining said shift member 307 in the prescribed set position involves a caster 309 supported under carriage body 302 rotatably around a vertical axis. Said caster has a caster wheel 309a with a pivot shaft 309b spaced to said axis on a horizontal plane. And said maintaining means further involves an actuator 310 having two set positions and connected with said shift member 307. Said actuator is shifted from one of said set positions to the other and viceversa via the shift member 307 by the traction power generated when the train of the trailers runs in a reverse direction, and maintains the shift member 307 at said set position by means described hereinafter when the caster is turned about said vertical axis by the caster wheel trailing on the ground.

The means for maintaining the shift member 307 at said set position is involved in said actuator 310, which comprises an actuator member 310a associated with said shift member 307 and movable in a direct line, two ratchet teeth 310b formed with both sides of said actuator member 310a, two ratchet members 3100 pivoted to the frame of said trailer body 302 and alternately engageable with said ratchet teeth 310b, and means for urging said ratchet members 3l0c to said actuator member, for example, a tension spring member 310d.

The caster assembly 309 further involves a bearing member 3090 supported by said trailer body 302 rotatably around a vertical axis and bearing said pivot shaft 309b, a turning cam 309d secured to said bearing member 3090 and alternately pushing the ratchet members to be disengaged from the corresponding ratchet teeth,

and means for urging said caster wheel downwards to be depressed to the ground.

In operation, when the train of the trailers runs in a reverse direction, the trailer body 302 is apt to be maintained in a stationary state and the shift member 307 is forcedly shifted by the traction power together with the actuator member 310a, so that until the actuator 310 travels to a set position, the pushing portions 305a of the engaging member 305 have access to and contact with the contact portions 304a of the steering member 304, whereby the steering member 304 is aligned with said engaging member 305. When the actuator reaches the set position, one of the ratchet members 310C is engaged with one of the ratchet teeth 3l0b in a direction opposite to that in which the train of trailers in drawn, with the caster wheel 309a turning about a vertical axis by the traction power.

FIG. 13 indicates a shifting action assembly modified from that of the first embodiment. Said shifting action assembly involves a manually operable handle lever 400 pivoted to the under portion of the trailer body by a vertical pivot 400a and which acts instead of that of the shift member and the caster assembly 21.

Since the other parts of said shifting action assembly are the same structures approximately as the first embodiment, the explanation of said parts is abbreviated for avoiding the complication, and said parts are illustrated only in the drawing by reference numbers involving the same digits as those of the parts of the first embodiment, together with four digits in a third place.

When the changing lever 400 is rotated to shift the slide member 413 via the shift means, said locking member 413 is set into a locking position thereby causing the corresponding steering member 410 to be forcedly fitted with the corresponding engaging member 412, and simultaneously another locking member 413 is guided to be released from a locking position thereby causing the corresponding steering member to be free from the corresponding engaging member.

What is claimed is:

l. A device for locking a tow bar together with a steering member of running wheels in a trailer which is adapted to be incorporated with other trailers to form a train, characterized in that said locking device comprises a vertical set pin secured to the end portion of a trailer body, a steering member rotatably supported by said set pin and having a longitudinal slit, an engaging member rotatably supported by said set pin and rigidly connected with one end of a tow bar, said engaging member having a slit which involves a locking portion and a releasing portion, a slide member inserted into said slits so as to be engaged with said engaging member at said locking portion'and disengaged from said engaging member at said releasing portion in connection with a circular direction in which said engaging member is rotated about said set pin, and means for automatically shifting said slide member from said locking portion to said releasing portion and vice versa, said shifting means having a caster supported under said trailer body rotatably around a vertical axis when said caster trails on the ground by traction power applied to the train of trailers.

2. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 1 in which said slit of the engaging member is formed substantially into a sectorial shape, at the basic point of which is positioned said locking portion of said slit.

3. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 1 in which said caster comprises a caster wheel with a pivot shaft, a supporting member disposed under said trailer body rotatably around a vertical axis so as to bear said pivot shaft and a turning cam secured to said supporting member, and an actuator having two set positions, said actuator involving a shift member associated with said slide member and moved in a direct line by the turning movement of said cam, with the resultant movement causing said actuator to be shifted from one of said set positions to the other and vice versa when the caster is turned about said vertical axis by the caster wheel trailing on the ground.

4. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 1 in which said caster has a caster wheel with a pivot shaft spaced to said axis on a horizontal plane, and an actuator having two set positions, said actuator being shifted from one of said set positions to the other and vice versa when the caster is turned about said vertical axis by the caster wheel trailing on the ground.

5. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 4 in which said shifting means further involves means for urging a caster wheel downwards to be depressed to the ground.

fi-Ad qplockins a owbam e r .wit a steering member of running sheels, characterized in that said locking device comprises two vertical set pins secured to both end portions of a trailer body respectively; steering members rotatably supported by said set pins respectively; engaging member rigidly connected with the corresponding tow bars respectively; a shift member disposed under the trailer body movably in a direct line; two locking members associated with said connecting member by means of link assemblies; a caster comprising a caster wheel with a pivot shaft, a supporting member disposed under said trailer body rotatably around a vertical axis so as to bear said pivot shaft and a turning cam secured to said supporting member; and an actuator having two set positions, said actuator being caused to be shifted from one of said set positions to the other and viceversa when the caster is turned about said vertical axis by the caster wheel trail ing on the ground, whereby one of said locking members is set into a locking position thereby causing the corresponding steering member to be forcedly fitted with the corresponding engaging member, and simultaneously the other locking member is guided to be released from a locking position thereby causing the cor responding steering member to be free from the corresponding engaging member.

YI INITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,853,330 Dated Desemben JD 191 Inventor It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 12, cancel "It" and substitute ---In--;

Column line cancel p itionedfi and substitute v ,"3 positio negi- Column 8, line 29, cancel "sheels" and substitute --whee1s Signed and sealed this 22nd day of April 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Comissioner of Patents Attesting Officer and Trademarks USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINTING OFFICE "I! 0-!6-331 F ORM F'O-OSO (10-69) 

1. A device for locking a tow bar together with a steering member of running wheels in a trailer which is adapted to be incorporated with other trailers to form a train, characterized in that said locking device comprises a vertical set pin secured to the end portion of a trailer body, a steering member rotatably supported by said set pin and having a longitudinal slit, an engaging member rotatably supported by said set pin and rigidly connected with one end of a tow bar, said engaging member having a slit which involves a locking portion and a releasing portion, a slide member inserted into said slits so as to be engaged with said engaging member at said locking portion and disengaged from said engaging member at said releasing portion in connection with a circular direction in which said engaging member is rotated about said set pin, and means for automatically shifting said slide member from said locking portion to said releasing portion and vice versa, said shifting means having a caster supported under said trailer body rotatably around a vertical axis when said caster trails on the ground by traction power applied to the train of trailers.
 2. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 1 in which said slit of the engaging member is formed substantially into a sectorial shape, at the basic point of which is positioned said locking portion of said slit.
 3. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 1 in which said caster comprises a caster wheel with a pivot shaft, a supporting member disposed under said trailer body rotatably around a vertical axis so as to bear said pivot shaft and a turning cam secured to said supporting member, and an actuator having two set positions, said actuator involving a shift member associated with said slide member and moved in a direct line by the turning movement of said cam, with the resultant movement causing said actuator to be shifted from one of said set positions to the other and vice versa when the caster is turned about said vertical axis by the caster wheel trailing on the ground.
 4. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 1 in which said caster has a caster wheel with a pivot shaft spaced to said axis on a horizontal plane, and an actuator having two set positions, said actuator being shifted from one of said set positions to the other and vice versa when the caster is turned about said vertical axis by the caster wheel trailing on the ground.
 5. A device for locking a tow bar together with a steering member of running wheels, claimed in claim 4 in which said shifting means further involves means for urging a caster wheel downwards to be depressed to the ground.
 6. A device for locking a tow bar together with a steering member of running wheels, c h a r a c t e r i z e d in that said locking device comprises two vertical set pins secured to both end portions of a trailer body respectively; steering members rotatably supported by said set pins respectively; engaging member rigidly connected with the corresponding tow bars respectively; a shift member disposed under the trailer body movably in a direct line; two locking members associated with said connecting member by means of link assemblies; a caster comprising a caster wheel with a pivot shaft, a supporting member disposed under said trailer body rotatably around a vertical axis so as to bear said pivot shaft and a turning cam secured to said supporting member; and an actuator having two set positions, said actuator being caused to be shifted from one of said set positions to the other and viceversa when the caster is turned about said vertical axis by the caster wheel trailing on the ground, whereby one of said locking members is set into a locking position thereby causing the corresponding steering member to be forcedly fitted with the corresponding engaging member, and simultaneously the other locking member is guided to be released from a locking position thereby causing the corresponding steering member to be free from the corresponding engaging member. 